Field of the Invention
The present invention relates to a vibration-type actuator that brings a vibrating body and a driven body into pressure contact with each other and moves the vibrating body and the driven body relatively to each other through driving vibrations excited in the vibrating body, and an electronic apparatus having the vibration-type actuator.
Description of the Related Art
There are known a variety of vibration-type actuators which bring a driven body into pressure contact with a vibrating body, which is constructed by joining an electro-mechanical energy conversion element such as a piezoelectric element to an elastic body together, and move the vibrating body and the driven body relatively to each other through driving vibrations excited in the vibrating body. For such vibration-type actuators, a method that brings the vibrating body and the driven body into pressure contact with each other using magnetic force is known. For example, an arrangement in which a permanent magnet is provided in at least a part of the driven body has been proposed (see Japanese Patent Publication No. 4072518 and Japanese Patent Publication No. 5349768). An arrangement in which a magnetic member is placed in a space between the vibrating body and the driven body has also been proposed (see Japanese Patent Publication No. 4881064). Specifically, a projecting portion which comes into contact with the driven body is provided on a first surface of the vibrating body, and a permanent magnet is placed between the first surface and the driven body so that the driven body can be attracted toward the vibrating body by magnetic force. A pressurizing mechanism using such a permanent magnet is more advantageous than a pressurizing mechanism using a spring because of a simplified structure.
FIG. 11A is a perspective view schematically showing an arrangement of a vibration-type actuator 70 with a pressuring mechanism according to a prior art. The vibration-type actuator 70 has a vibrating body 77 constructed by forming a piezoelectric element 72 integrally with an elastic body 71, which is made of a ferromagnetic material, using an adhesive agent, and a permanent magnet 74. The permanent magnet 74 is in pressure contact with a part of the elastic body 71, and driving vibrations excited in the vibrating body 77 move the permanent magnet 74 and the vibrating body 77 relatively to each other.
FIG. 11B is a cross-sectional view showing a state in which the permanent magnet 74 and the vibrating body 77 are in pressure contact with each other. It should be noted that in FIG. 11B, the cross-section of the permanent magnet 74 has a substantially rectangular shape, and the elastic body 71 and the permanent magnet 74 move relatively to each other in a direction perpendicular to the sheet of the figure. The permanent magnet 74 is magnetized in a horizontal direction as viewed in FIG. 11B, and a magnetic action of the permanent magnet 74 and the elastic body 71 is indicated by magnetic lines of force I in FIG. 11B. An attracting action resulting from the magnetic lines of force I passing through the permanent magnet 74 and the elastic body 71 generates a pressurizing force on the elastic body 71 and the permanent magnet 74.
A variety of apparatuses equipped with a vibration-type actuator are always required to be downsized and implement high-density packing, and a pressuring mechanism of a vibration-type actuator as well is required to be further downsized. An output from a vibration-type actuator, in particular, generative force (torque) from a vibration-type actuator depends on frictional force generated between a vibrating body and a driven body, and therefore, in order to obtain required generative force, a pressurizing mechanism capable of generating desired pressurizing force is needed between a vibrating body and a driven body. For example, in the vibration-type actuator 70 in FIGS. 11A and 11B, a significant amount of magnetic lines of force I does not pass through the elastic body 70. In particular, since no arrangement that guides the magnetic lines of force I is provided on an upper side of the permanent magnet 74, many magnetic lines of force I do not pass through the elastic body 71, and hence magnetic force of the permanent magnet 74 cannot be effectively used. For this reason, to obtain required pressurizing force, there is a limitation on the extent to which the size or the like of the permanent magnet 74 is reduced, and it is thus uneasy to downsize the pressurizing mechanism.